Phenol is an important product in the chemical industry and is useful in, for example, the production of phenolic resins, bisphenol A, ε-caprolactam, adipic acid, and plasticizers.
Currently, the most common route for the production of phenol is the Hock process. This is a three-step process in which the first step involves alkylation of benzene with propylene to produce cumene, followed by oxidation of the cumene to the corresponding hydroperoxide and then cleavage of the hydroperoxide to produce equimolar amounts of phenol and acetone.
However, the various steps involved in the production of phenol and acetone from cumene can produce various contaminants that are difficult to separate from the desired phenol and acetone products. Examples of these contaminants may include hydroxyacetone, mesityl oxide, 2-methylbenzofuran, acetophenone, alpha-methylstyrene, cumene, 2-phenylpropanal.
These contaminants, if left in the phenol product, may cause difficulties in downstream processing, or render the phenol unusable for such downstream processing, for example in the subsequent production of bis-phenols and polycarbonates. Therefore, techniques have been proposed to remove those contaminants involving certain treatments. For example, U.S. Pat. No. 5,064,507 discloses obtaining high purity phenol from cleavage of cumene hydroperoxide through one or more amine treatment steps. The phenol mixture includes at least 0.5 wt % to no greater than 10 wt % of alpha-methylstyrene, and further includes acetol, 2-phenyl-propionaldehyde (2PPA), methyl-benzofuran (MBF), mesityl oxide (MO) and carbonyl impurities. In addition, U.S. Pat. No. 3,322,651 discloses a method of producing phenol made by decomposition of cumene hydroperoxide. The phenol is purified by contacting the carbonyl compounds with a nitrogen compound.
The production of phenol from cyclohexylbenzene is an emerging technology, interesting in that it co-produces cyclohexanone rather than acetone. Cyclohexylbenzene can be produced, for example, by direct alkylation of benzene with cyclohexene, or as disclosed in U.S. Pat. No. 6,037,513, by contacting benzene with hydrogen in the presence of a catalyst. The cyclohexylbenzene can then be oxidized to the corresponding hydroperoxide and the peroxide cleaved to phenol and cyclohexanone using an acidic cleavage catalyst.
One problem of producing phenol by way of the cleavage of cyclohexylbenzene hydroperoxide is that the cyclohexanone and phenol produce an azeotropic mixture composed of 28 wt % cyclohexanone and 72 wt % phenol. Thus, any attempt to separate the cleavage effluent by simple distillation results in this azeotropic mixture. To obviate this problem it has been proposed to integrate the cyclohexylbenzene oxidation and cleavage process with a dehydrogenation step whereby at least part of the cyclohexanone is converted to additional phenol (see International Patent Publication No. WO2010/024975). Such a dehydrogenation step is generally achieved by contacting the cyclohexanone with a supported metal catalyst at a temperature of about 250° C. to about 500° C.
The production of phenol from cyclohexylbenzene also produces various contaminants that are difficult to separate from the desired products. However, the nature of those contaminants and the separations involved are significantly different than those involved in the conventional Hock process for phenol and acetone. For example, hydroalkylation of benzene produces significant amounts of, inter alia, cyclohexane and lesser amounts of methylcyclopentane, cyclohexene, phenylcyclohexene, and phenylcyclohexyldiene. Similarly, the oxidation of cyclohexylbenzene typically produces peroxide species alien to the Hock process, such as the desired cyclohexyl-1-phenyl-1-hydroperoxide (CHBHP), and undesired byproduct hydroperoxides such as cyclohexyl-1-phenyl-2-hydroperoxide, cyclohexyl-1-phenyl-3-hydroperoxide, and cyclohexyl-1-phenyl-4-hydroperoxide. Similarly, the cleavage of these various hydroperoxides produces, as both the product of the undesired hydroperoxides and the undesired byproducts of the desired CHBHP, a wide variety of contaminant species are not produced by the chemistry and technology of the Hock process. Similarly, the dehydrogenation of cyclohexanone to phenol typically produces various hydrocarbons such as hexanone, cyclohexenol and methylcyclopentenone.
That said, provided herein are methods for producing phenol and cyclohexanone from cyclohexylbenzene and dehydrogenating a portion of the cyclohexanone into phenol. Further described are methods for managing the contaminants that are generated in the above-described process.
Advantageously, the methods described herein produce high-quality phenol compositions that are novel, useful and very different from those typically produced by conventional methods (e.g., the Hock process). The chemistry associated with cyclohexylbenzene as a starting material in the instant invention, and further the complete absence of cumene and its conversion products and byproducts, potentially provides a phenol composition with contaminants that are of a markedly different type and concentration than the conventional methods. These contaminants may be less problematic in further processing, e.g., to phenolic resins. Moreover, the contaminants produced in the processes described herein have lower volatility compared to contaminants produced by conventional methods, and therefore may be present in lower concentrations.